Depth Affects Algal Symbiont Composition in Caribbean Coral

NCCOS-funded researchers investigating the diversity of symbiotic algae (Symbiodinium spp.) associated with the coral Agaricia lamarcki in Puerto Rico and the U.S. Virgin Islands found the coralís algal associations change with depth.

Light-dependent corals form a mutually beneficial relationship (symbiosis) with the single-celled algae Symbiodinium, commonly known as zooxanthellae, which provide energy for the coral through photosynthesis. There are a variety of species of Symbiodinium which have different tolerances for light and temperature, and these traits determine the ability of coral to thrive under warmer conditions. Corals in shallower depths are at a greater risk. For the very abundant coral A. lamarcki, although found in both shallow and mesophotic depths (10-100 m) throughout the Caribbean, its ability to replenish depleted shallower reefs (10-40 m) may depend on the algae type it houses.

This is the first reporting of the presence of the thermal-tolerant species,†Symbiodinium trenchii, in the upper layers of the coralís depth range (20-25 m). This finding raises hope that A. lamarcki corals associated with S. trenchii living in the depleted shallower reefs (10-40 m) may be adapting to changing environmental conditions.